This study is an open-label, 6 month trial, of immediate release methylphenidate (MPH-IR) for children with ADHD aimed at assessing whether the observable behavioral changes seen during treatment are associated with potentially more stable underlying modifications in brain functioning (resting-state functional connectivity). Additionally, we will also be looking at treatment effects on neuropsychological processes and reading skills. This information will contribute to the first Brazilian study assessing the cost-effectiveness of the treatment of ADHD. Children with ADHD will be compared to a sample of sex and age-matched sample of typically developing children.